1. FIELD OF THE INVENTION
The present invention relates to a recording taps cartridge and more particularly to an arrangement for preventing deformation of the recording tape cartridge.
2. DESCRIPTION OF THE RELATED ART
Recording tape cartridges so called compact cassettes or philips type tape cassettes are usually formed of plastic resin materials using resin injection molding. FIGS. 1 and 2 show one example of a conventional recording tape cartridge of the above type in which a cartridge case 1 is formed by assembling a bottom half 1a and a top half 1b in a butting manner and both of the halves are connected together by screws. Both of the halves 1a and 1b are formed almost in a similar shape having a front wall 2, side walls 3 and rear wall 4 each projected from a main plate 1x. A pair of drive shaft insertion holes 7a are defined in the main plate 1x with a predetermined interval and a window 7b of a square shape is defined between the drive shaft insertion holes 7a so as to see the amount of the roll of recording tape 5 wound on respective tape hubs 6 rotatably mounted on the drive shaft insertion holes 7a. A head insertion opening 8 is defined on the central portion of the front wall 2. A partition wall 10 is formed extending in a lateral direction or in a direction towards both side walls 3 of the case 1 at the inside of the half 1a (or 1b) so as to separate the head insertion window 8 and a tape chamber 9. Each pairs of tape guide members 11, 12 and 13 are provided symmetrically on the main plate 1x between the front wall 2 and the partition wall 10 along a tape path.
In molding the respective top and bottom halves 1a and 1b, it is necessary to form particularly the respective tape guide members 11, 12 and 13 in the front portion of the case 1 with a high precision of molding. Therefore, usually an injection gate G for injecting plastic resin into a mold is provided near the front side of each of the halves. In case plastic resin is injected into the mold through the gate G, the paths of the injected plastic resin flow in the mold generally are shown by lines A in FIG. 2 and there tends to occur resin orientation. In addition, recently there has developed a strong requirement of decreasing thickness of the respective walls of the cartridge and high cycle molding and therefore, the work of injection of the cartridge must be made with high speed, whereby the resin orientation would be promoted.
Furthermore the resin flow, as shown by the lines A flowing along the drive shaft insertion holes 7a and the window 7b, meets together after the resin flows pass the drive shaft insertion holes and window. As a result, there tends to be undesirably formed weld marks W, as shown in FIG. 2, and therefore, in case the cartridge having the weld mark and/or resin orientation is put under high temperature, the cartridge is easily bent or twisted at the position where the resin orientation and/or weld marks are strong. Particularly bending of the cartridge along the flow of the resin easily occurs. If the tape cartridge is undesirably bent or twisted the parallelism and flatness of the cartridge are harmed, whereby tape running becomes unstable and the recording and reproducing characteristics of the tape cartridge are badly affected.
Japanese Utility Model Publication 153685/1984 disclosure providing a number of ribs in a tape cartridge for the purpose of increasing the mechanical strength of the tape cartridge, but there is no contrivance of improving the resin flow to eliminate the resin orientation and weld marks.